One of the most realistic strategy games I've ever played. And so rich of details and micromanaging!
Every unit are made of several squads of different types put together. All these have their special capacities. Every singe unit depends strengths and weaknesses depends on what squads that are present. Lack of vehicles for example gives lower rate of resupply, witch is important for the battle readiness, and can decide the outcome of a battle. A unit can, depending on the scenario, have up to maybe 200 squads, some times of 25 different types. In a scenario you therefore sometimes can command more than 10.000 squads of fifty or more different types.
Reconnaissance. Depends on several factors, how many specialized recon units and vehicle present are the most important. This impacts on how much you know about an nearby enemy unit.
Mobility. Mostly depends on how big part of the unit that are vehicles, how mobile every single unit are, and how the terrain are. Some squads requires transport, and the unit won't move if you lose all your transport. If you only have a small number of transports, the movement will be slow, and the unit will resupply slowly. If other unit's are present whit large amounts of transports, I believe it's possible to move otherwise static units. Movement costs also changes if you move close to an enemy unit.
Attack strength. There are tree types, anti personal, anti armour and artillery. Attack strength, like everything else, also depends on the supply level and unit readiness.
Defence. This is very dependant on environmental and supply factors, as well as what type of squads present. Some squads are passive and some are active defenders. Passive, such as mortars, machine guns and trucks are more vulnerable to flank attacks. There's some types of defence strengths. These are anti air, low and high altitude, and "normal" defence, active OR passive.
Supply. This means the unit's storage of fuel, munitions, food, and everything an army need. Low supply levels lower the morale and unit readiness. Every time a unit moves or fights, the supply levels sinks. It's raisin slowly each turn. The supply levels raises more quickly near a supply base, if there's good roads or rails leading to a supply base, and if there's many vehicles present in the same or adjacent square. So don't let your enemy flank you too often, and you'll loose too many, often passive units used for transport.
Unit readiness. Simply how well prepared a unit are to go into battle. lowered when moving, when there's low supply levels, and the enemy plays are fighting you.
Morale. Lowered after large losses, and when the supply levels are low.
Engineer abilities. Engineers are important for an effective use of your army. There's different types of specialized engineers. Rail repairing, minor ferry, major ferry, and other engineering. Unit whit many engineers whit minor or major (especially for large rivers and shallow waters) ferry are especially useful to place on a river before crossing it whit other units, giving a reduction in the action points needed to cross the river.
Guerilla. Guerilla units have special qualities. They can resupply much better when out of normal supply lines. They only change ownership in squares where they stay, making them harder to see.
New units. There's no way to create new units. But for every scenario, there will often new units arrive. You know this, as they're listed in the "expected reinforcement" menu. In many scenarios, destroyed units can recompose, if there's enough of the needed squads in the inventory.
Lost squads. Lost squads can be replaced if they're available in the inventory. The rate of which they're replaced depends on how well the unit are supplied. Good roads and allot of transports means fast replacements. In the inventory menu, it's showed how much squads are available for replacement, and at which rate they're created. Some units, often older ones, are available in great numbers, but are not filled up. Some are not available in the beginning, but will later drop in in large numbers. Trying to save single types of squads, when managing large number of units is a difficult task.
Transport by air, rail or sea depends on how heavy your units are, and the transport points for each type available. This changes for every scenario, and often during a scenario.
Entrenchments and fortifications are made in the terrain, not in the unit as in many other games. Dig in whit an engineer unit, place another units there, and move your engineers to another square. All units can dig, but some do it faster than others.
Both time and scale wary between the scenarios. Sometimes a square means 2,5 km, sometimes allot more.
You can play in most wars from Waterloo 1815 to an hypothetical invasion of Taiwan 2015. There's many scenarios, and if there's still not enough, you can design your own.
All this factors make it almost impossible to do anything exactly the same way more than one time. No battle looks like another.
Maybe the best thing is the supply system. In many game, you can hold out for years far inside enemy territory, without losses. In this game it's possible to leave weaker forces being the lines and let them starve to death.
This complexity also require allot of time. When I started playing a scenario in south Vietnam as north Vietnamese, the first turn took me some 15 hours!
This is why the game is so hard. Don't begin on normal level, unless you're an officer of higher ranks...
This is also why this game can be a little bit boring sometimes. It's simply too hard. But so are the reality too. And there's almost nothing in this game that would have been better made. The graphics are not so good, and I can't hear any sounds (I'm using Vista). But this is a strategy game, there's no need for good graphics. And this makes the game easy to run on old computers.